This application is based on, and incorporates herein by reference, Japanese Patent Application No. 2001-99674 filed on Mar. 30, 2001.
1. Field of the Invention
The present invention relates to a valve timing control device for adjusting the timing in opening an intake valve or an exhaust valve of an internal combustion engine. More specifically, the invention relates to a vane-type valve timing control device having a torsion spring for applying a rotational load between a shoe housing and a vane rotor.
2. Description of Related Art
In general, a vane-type valve timing control device comprising the following configuration is known in the art. That is, such a device comprises a shoe housing rotatably arranged with a crank shaft (corresponding to a drive shaft) and a vane rotor rotatably arranged with a cam shaft (corresponding to a driven shaft) for rotating the vane rotor relative to the shoe housing. Also, the vane rotor has a plurality of vanes which are provided with the cam shaft and which extend outwardly from the vane rotor in the radial direction into chambers formed in the shoe housing. The vanes divide each chamber into advancing chambers and delaying chambers. The vane rotor can be hydraulically rotated within the shoe housing between the advancing chamber and the delaying chamber causing the cam shaft to shift to the advancing side or the delaying side.
When the engine is running, the cam shaft can be driven to the advancing side by sequentially transmitting torque to the shoe housing, the vane rotor, and the cam shaft. In other words, the vane rotor receives a load in the advancing direction. Therefore, when the vane rotor rotates to the advancing side or the delaying side, the response of the relative rotation to the advancing side can be decreased compared with the relative rotation to the delaying side.
If the valve timing control device is mounted on the cam shaft on the exhaust side, the duration of simultaneously opening the inlet valve and the exhaust valve becomes longer than required when the exhaust side cam shaft is located at the delaying position together with the inlet side cam shaft when the engine is started. Consequently, there are problems during startup.
For solving such a disadvantage, other conventional valve timing control devices have been disclosed. Unexamined Japanese Patent Publication (Kokai) Nos. Hei 11-294121 (1999), 10-252420 (1998), and 11-132014 (1999) disclose such devices. In each of these publications, there is disclosed technical means of engaging the ends of a torsion spring with a shoe housing (or a member rotatable together with the shoe housing) and a vane rotor, respectively, to urge the vane rotor relative to the shoe housing in an advancing direction.
In the conventional valve timing control device disclosed in each of those publications, both ends of the torsion spring are directed in the axial direction of the torsion spring. The vane rotor has an axial opening for engaging an axial end of the torsion spring. In this case, however, the formation of such an axial opening requires an increase in the axial thickness (cross-section) of the vane rotor, and limits any reduction in physical size of the valve timing control device with, say, a vane rotor with a smaller cross-section.
As shown in FIG. 9, for example, there is shown one end J3 of the torsion spring J2 to be engaged with the vane rotor J1. The end J3 is formed to extend outwardly in the radial direction of the torsion spring J2. A hook groove J4 for engaging the end J3 of the torsion spring J2 is formed in the vane rotor J1.
In this case, however, in FIG. 9, the hook groove J4 is formed in the vane J5 when the hook groove J4 is extended outward in the radial direction of the torsion spring J2. As a result, problems such as a decrease in the strength of such a vane J5 are caused. In addition, the length of a seal with the vane J5 is shorter, so that the degree of sealing between the advancing chamber J6 and the delaying chamber J7, partitioned by the vane J5, can be decreased when the vane J5 is made smaller for advantageously making the overall size of the valve timing control device smaller.
On the other hand, if the vane rotor is displaced to the advancing side or the delaying side, there is a possibility that the position of the torsion spring may be changed because of the variation in spring load applied on the torsion spring. When the spring load changes, the coiled portion of the torsion spring becomes inclined, skewed, or eccentric from the axial center of the coiled portion because the torsion spring tries to keep its appropriate position for the changing load.
It is conceivable that the torsion spring will not generate predetermined torque when the coiled portion of the torsion spring becomes inclined or eccentric. Additionally, it is also possible that the torsion spring may make contact with another component and the component will inappropriately wear due to, say, vibrations or rubbing created by the coiled portion that is inclined or eccentric.
Accordingly, it is a first object of the present invention to provide an improved valve timing control device having a torsion spring: (A) for urging the vane rotor relative to the shoe housing toward the advancing side or the delaying side; (B) for preventing the vane rotor within the shoe housing from being overly large in cross-section, or thick; (C) for preventing a decrease in the strength of a vane placed between the advancing chamber and the delaying chamber; and (D) for preventing a decrease in the sealability of the advancing chamber and the delaying chamber with the vane by providing an engaging means for the torsion spring.
A second object of the present invention is to provide an improved valve timing control device having a torsion spring: (A) capable of preventing the inclination or eccentricity of a coiled portion of the torsion spring due to the variation in spring load applied to the torsion spring; (B) capable of generating a constant, predetermined amount of torque; and (C) capable of preventing wear on an unexpected part caused by loading on the torsion spring.
In a first embodiment of the present invention, a valve timing control device is mounted on a power transmission system for transferring power from a drive shaft of an internal combustion engine to a driven shaft for opening and closing a valve. The device causes a phase difference between the rotation of the drive shaft and the rotation of the driven shaft. Additionally, there is a shoe housing having a chamber, the shoe housing being rotatable together with one of the drive shaft and the driven shaft, a vane rotor being rotatable together with the other of the drive shaft and the driven shaft, the vane partitioning the chamber formed in the shoe housing into an advancing chamber and a delaying chamber. Furthermore, there is a torsion spring having one end engaged with the shoe housing or a member rotatable together with the shoe housing and the other end engaged with the vane rotor or a member rotatable together with the vane rotor to urge the vane rotor relative to the shoe housing toward an advancing side or a delaying side. The other end of the torsion spring engaged with the vane rotor or the member rotatable together with the vane rotor is provided as an inwardly-directed end which is inwardly directed in the radial direction of the torsion spring, and the vane rotor or the member rotatable together with the vane rotor has a hook groove with which the inwardly-directed end of the torsion spring is engaged.
The hook groove for engaging the torsion spring is formed to extend inwardly in the radial direction of the torsion spring. In other words, the hook groove is not formed in the inside of the vane for partitioning the advancing chamber and the delaying chamber. This makes it possible to prevent compromising the strength of the vane while decreasing the size of the vane rotor. Additionally, the hook groove is formed as described above, so that the wearing away of the vane rotor in contact with the torsion spring can be prevented even though the vane rotor is made of a low hardness material such as aluminum or soft iron.
In the second aspect of the present invention, a valve timing control device can be operated without the torsion spring becoming out-of-balance. Inclination or eccentricity of a coiled portion of the torsion spring, with respect to a shaft center, will not occur even though the spring load applied on the torsion spring may vary as the vane rotor is displaced to the advancing or delaying side. This makes it possible to generate a predetermined amount of torque constantly by the torsion spring regardless of the variation in spring load applied on the torsion spring. Also, premature wearing of other parts by the torsion spring contacting with other parts will not occur.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.